Substantial savings of time and money have been realized in the industry by handing a plurality of printed circuit boards (PCB's) while they are still interconnected in a panel of substrate material. Better utilization is realized with this approach in such processing as population of the PCB's with components, wave soldering of the populated boards, and quality control such as electrical function testing of whole boards or selected components, particularly when considering the automated processing demands of today's industry.
Methods for enabling separating of each prepopulated panel into plural, individual PCB's include: routing with tabs; scoring; perforation; and punch-back.
Routing with tabs comprises routing slots in the panel (while leaving spaced support tabs) to define the perimeters of the individual boards, so that the tabs may be cut or broken in order to perform board separation.
Scoring comprises grooving board perimeters on at least one side of the panel in order to effect board separation by breaking along the score-lines.
Perforation comprises drilling a series of closely spaced holes in the panel along the board perimeters so that board separation is performed by breaking along the lines of perforations.
The punch-back method utilizes a custom-made die to punch each board out of the panel and then pull it back into the panel so that, after population, the boards are easily pushed from the panel.
All of these "break-away" methods of preparing panels, for subsequent separation of the populated PCB's, inherently rob the panel of its rigidity. Consequently, the panels are prone to: sagging during wave soldering; excessive warping; and premature breakage. Moreover, methods incorporating excessive treatment by a router are expensive, can permit solder to overflow onto the component side of the panel during wave soldering, and often can require a secondary procedure for removing tab stubs. Perforation and scoring yeild poor quality edges and cannot hold close tolerances. Punch-back methods require expensive tooling and cannot process zero-spaced configurations, i.e., panels without scrap strips between adjacent circuit boards. Premature separation during panel handling is frequently encountered with the punch-back and scoring methods.
Whether or not the boards have been populated, high precision shearing is recognized as a preferred, cost-effective method for PCB profiling by separating individual boards from the panels. The shock to delicate components and traces, normally encountered during the separating of boards from panels by breaking along perforation or score lines, can be obviated by shearing blade configurations. Further, a panel may be gently sheared without the shock of other methods, while providing excellent edge quality and holding board perimeter tolerances within 0.005 inches, repeatedly. Since there are no tab stubs to be removed with the shearing method, the circuit boards often can be zero-spaced (without waste strips) in order to provide more boards per panel. In fact, many rectangular boards can be sheared in less time than it takes to cut the same run with an NC router, while irregular boards can be cut by combining the routing and shearing methods to minimize the routing and maximize panel rigidity. The clean, simple edges provided by shearing also enhances computer aided design and manufacturing (CAD/CAM).